Polymerization of 3,4-difluoropyrrole: Electrochemical and physicochemical behavior of poly(difluoropyrrole)

The electrochemical polymerization of 3,4-difluoropyrrole (DFP) has been examined by cyclic voltammetry (CV) as a function of scan rate and solvent. The polymerization is facile in dichloroethane, leading to a stable electroactive film. In contrast, the corresponding polymerization in acetonitrile occurs only with difficulty. Poly(3,4-difluoropyrrole) (PDFP) exhibits a high redox potential (+0.90 V vs Ag/AgCl), a particularly high doping level (ca. 55%,), and a rather good conductivity (up to 0.1 S.cm(-1)), in comparison to other polyhalopyrroles. Meanwhile, the lifetime of the DFP radical cation, as determined by fast scan CV experiments, is about 1 ms. This lifetime is substantially longer than that of other pyrrole derivatives under identical experimental conditions. Theoretical calculations are in agreement with experiment in showing that the DFP radical cation is a powerful oxidant in comparison to pyrrole radical cation. However, these computational studies indicate that the net charge and spin distributions are similar for the cation radicals of DFP and pyrrole itself. To interpret these results, we propose that the introduction of fluorine substituents could be responsible for a lower polarizability of the cation radical, leading to a higher activation barrier for dimerization of DFP in comparison to pyrrole and other halopyrroles.